Matrix-assisted Laser Desorption/ionization Mass Spectrometry of Deoxynucleotides Labeled with an IMI Dye

The four major deoxynucleotides of DNA, and adduct mixtures resulting from separate reactions of 5'-dAMP and 5'-dGMP with benzo[a]pyrene diolepoxide (BPDE), were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) after labeling of their phosphate group with an IMI dye. The latter reagent comprises an imidazole functional group attached to a BODIPY (4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene+ ++) fluorophore. Good sensitivity was observed in the detection of the IMI-labeled products by MALDI-MS: 300-500 fmol in the laser spot (1% of the 30-50 pmol sample on the target) gave a signal-to-noise (S/N) of >/=30 from 20-30 superimposed laser shots. The BPDE reaction products, after the IMI labeling, were also subjected to capillary electrophoresis with laser-induced fluorescence detection, which revealed a complex mixture of products. Overall the results encourage the further development of this 'IMI-postlabeling' methodology as an alternative to (32)P-postlabeling for the detection of DNA adducts.